The Production of (alpha,n) Neutrons for Plutonium in Glass

The Pacific Northwest Laboratory’s NonDestructive (NDA) group recently performed an initial study of neutron production in glass samples containing plutonium. The original PuO2 sources were counted in a neutron coincidence counting system. The Pu sources were then mixed into two different borosilicate glass samples and the samples were again counted in the same system. The samples exhibited significant increases in neutron count rates. The first glassified sample emitted neutrons at a rate of 11.1 times higher than the pure PuO2; the second glassified sample showed a factor of 13.5 increase over the original Pu sample. The increases in neutron emission can be explained by (alpha,n) reactions on the low-Z nuclei in the glass. The neutron production from (alpha,n) reactions exceeds that from spontaneous fission in this case. The results of the measurements are compared against theoretical calculations which predict (alpha,n) and spontaneous fission neutron production for plutonium mixtures. Neutron emission rates from plutonium and other TRU isotopes are typically used for characterizing the TRU contents of waste drums and packages; therefore, an accurate model for predicting the magnitude of (alpha,n) neutron production is essential for interpreting NDA results.